This invention relates to flame retardant compositions containing at least one tetrahalophthalate ester and a polycarbonate resin. Additionally this composition may also contain one or more brominated and/or chlorinated compounds in an amount to provide additional flame retardancy to the polycarbonate resin. This invention also comprehends the method of improving the flame retardancy and processability of the polycarbonate resins by using these tetrahalophthalate esters alone or in combination with one or more bromine and/or chlorine compounds.
Polycarbonate resins are known in the art as a class of thermoplastics that are characterized by excellent properties such as electrical, dimensional stability, high impact strength, toughness, and flexibility. In general, they are prepared by the reaction of a dihydric phenol with a carbonate ester, phosgene, or a bis chloroformate ester. U.S. Pat. Nos. 2,999,835; 3,169,121; 3,879,348; 4,477,632; 4,477,637; 4,481,338; 4,490,504; 4,532,282; 4,501,875; 4,594,375; and 4,615,832 describe in detail the preparation of various classes of polycarbonate resins, the teachings of which are incorporated herein by reference.
Because of their many excellent properties, polycarbonate resins are useful in many commercial applications as engineering thermoplastics and in the manufacture of molded articles.
The use of brominated and/or chlorinated compounds by themselves or in combination with other materials such as organic phosphates, antimony compounds, etc. as flame retardants for polycarbonate resin compositions are well known in the art and are exemplified by U.S. Pat. Nos. 3,334,154; 4,481,338; 4,533,690; 4,552,911; 4,576,991; 4,581,404; 4,626,563; and 4,632,953. The aforesaid patents are incorporated herein by reference.
Tetrahalophthalate esters have been used as flame-proofing materials. For example, U.S. Pat. No. 4,098,704 describes the use of these materials as textile finishing agents. U.S. Pat. Nos. 4,298,517 and 4,397,977 disclose these compounds as flame retardants for halogenated resins. However, no teaching have been found which show these compounds as flame retardants or processing aids for polycarbonate resins.